1. Field of the Invention
The present invention relates to the field of telecommunications. More particularly, the present invention relates to an apparatus and a method for enhancing telecommunications service provided by a digital wireless communications system.
2. Description of the Related Art
There is a rapid voice signal quality deterioration experienced with digital wireless communications systems when a received signal-to-interference ratio (SIR) is below a minimum SIR, or when a bit error rate is exceeded at a wireless station. The rapid deterioration experienced in voice quality results in the received signal being interspersed with audible clicks and pops, causing difficulty for a digital wireless user in understanding received voice signals.
FIG. 1 shows a graph of voice signal quality versus average RF signal-to-interference ratio comparison of IS-54 digital and analog FM performance at a wireless station. In FIG. 1, curve 10 represents the voice signal quality for an IS-54 wireless station as a function of average RF SIR. The voice signal quality shown by curve 10 is fairly constant for signal-to-interference ratios greater than about 17 dB (point 10a). For SIRs below about 17 dB, the voice signal quality rapidly deteriorates with decreasing SIR. At an SIR of about 14 dB, the voice signal quality of an digital wireless station falls below an acceptable level. Curve 11 in FIG. 1 represents the voice signal quality of an analog FM wireless station as a function of average RF SIR. The voice signal quality shown by curve 11 is fairly constant for signal-to-interference ratios greater than about 26 dB (point 11a). For SIRs below about 26 dB, the voice signal quality deteriorates with decreasing SIR. At an SIR of about 17 dB, the voice signal quality of an analog FM wireless station falls below an acceptable level.
As shown in FIG. 1, when the SIR of a received digital signal drops, the quality of the voice signal deteriorates an accelerated rate. When a digital wireless station has a call-waiting feature capability, an incoming call tone received during poor voice signal quality and coinciding voice communications may be misinterpreted by a user as part of an on-going noise disruption. Consequently, the incoming call tone may be improperly ignored by the user.
What is needed is a way to simulate the fading characteristic of an analog FM wireless station for a wireless digital communications station, and to indicate that a call waiting signal has been received when a received SIR of a voice signal is below a predetermined threshold.